Surface emitting semiconductor laser

ABSTRACT

A surface emitting semiconductor laser capable of improving high temperature properties is provided. In a surface emitting semiconductor laser, as well width of an active layer is set at from 4 nm to 6 nm and the number of wells thereof is set at one or two In addition, above and below the active layer, InGaAlP clad layers are formed, and in a stacking direction of the active layer, through the above and below clad layers each, further above and below thereof, light reflecting layers are formed.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromthe prior Japanese Patent Application No. 2000-353113, filed on Nov. 20,2000; the entire contents of which are incorporated herein by reference.

BACKGROUND

1. Field of the Invention

The present invention relates to a surface emitting semiconductor laser,and is suitably applicable particularly to an InGaAlP quantum wellstructure surface emitting semiconductor laser.

2. Description of the Related Art

Recently, a semiconductor laser emitting in the range of wavelengthsfrom 600 to 700 nm has been put into practical use in a field such asDVD (digital versatile disk) or the like.

Meanwhile, a surface emitting semiconductor laser, if being put intopractical use in this wavelength region, will be used as a light sourcefor a high speed plastic fiber link. As a surface emitting semiconductorlaser realizing such wavelength region, there is an InGaAlP surfaceemitting semiconductor laser. In order to lower a threshold current ofthe InGaAlP surface emitting semiconductor laser, there is a surfaceemitting semiconductor laser in which active layer a quantum wellstructure is adopted.

FIG. 10A is a perspective view showing a configuration of an existingInGaAlP quantum well surface emitting semiconductor laser. In FIG. 10A,on an n-GaAs substrate 1, there are stacked in turn a DBR (DistributedBragg Reflector) multi-layer film 2, an n-InGaAlP clad layer 3, an MQW(Multiple Quantum Well) active layer 4, a p-InGaAlP clad layer 5, a DBRmulti-layer film 6, and a p-GaAs cap layer 7. On a back surface of then-GaAs substrate 1, there is formed an n-side electrode 8, on the p-GaAscap layer 7 there being formed a p-side electrode 9. In the p-GaAs caplayer 7 and the p-side electrode 9, there is formed a disk like openingto form a light exit window 10 for taking out emitted light.

The active layer 4 is formed ofIn_(0.5)Ga_(0.5)P/In_(0.5)(Ga_(0.5)Al_(0.5))_(0.5)P film; the clad layer3 being formed of an n-In_(0.5)(Ga_(0.3)Al_(0.7))_(0.5)P film; the cladlayer 5 being formed of a p-In_(0.5)(Ga_(0.3)Al_(0.7))_(0.5)P film; theDBR multi-layer film 2 being formed of ann-Ga_(0.5)Al_(0.5)As/Ga_(0.05)Al_(0.95)As film; the DBR multi-layer film6 being formed of a p-Ga_(0.5)Al_(0.5)As/Ga_(0.05)Al_(0.95)As film.

Furthermore, the active layer 4 and the clad layers 3 and 5 form aresonator of the surface emitting semiconductor laser, and at the activelayer 4 in the center a film thickness is designed to be an antinode ofa standing wave of one wavelength.

FIG. 10B is an enlargement of a portion of the active layer and the cladlayers in FIG. 10A. In FIG. 10B, the MQW active layer 4, which is formedby repeating to alternately stack an In_(0.5)(Ga_(0.5)Al_(0.5))_(0.5)Pfilm 4 a and an In_(0.5)Ga_(0.5)P film 4 b, is sandwiched by the cladlayers 3 and 5 to form a double heterostructure junction.

FIG. 10C is an energy band diagram of a portion of the active layer 4and the clad layers 3 and 5. In FIG. 10C, the In_(0.5)Ga_(0.5)P films 4b being smaller in their band gaps in comparison with theIn_(0.5)(Ga_(0.5)Al_(0.5))_(0.5)P films 4 a, there are formed quantumwells QW at the portion of the In_(0.5)Ga_(0.5)P films 4 b. In thequantum wells QW, energy levels are quantized, and thereby energy levelsof electrons injected into the active layer 4 may be localized. As aresult, the laser may be efficiently oscillated, the threshold currentbeing lowered.

In addition, the clad layers 3 and 5, which are formed of then-In_(0.5)(Ga_(0.3)Al_(0.7))_(0.5)P film, are larger in their band gapsthan those of the In_(0.5)Ga_(0.5)P/In_(0.5)(Ga_(0.5)Al_(0.5))_(0.5)Pfilms. As a result, electrons and holes injected through the clad layers3 and 5 may be confined inside the active layer 4, the laser beingefficiently oscillated.

In the existing MQW structure surface emitting semiconductor laser, inorder to enhance a gain, it is general to set a well width Hb at 7 nm ormore and the number of wells Wn at five or more. However, in the activelayer 4 adopting the MQW structure, when the well width is 7 nm or moreand the number of the wells is five or more, heat generation from theactive layer 4 becomes larger, resulting in deterioration of hightemperature properties.

The object of the present invention is to provide a surface emittingsemiconductor laser capable of improving the high temperatureproperties.

SUMMARY

A surface emitting semiconductor laser according to an embodiment of thepresent invention includes an active layer having an InGaAlP quantumwell structure of which well width is from 4 nm to 6 nm and of whichnumber of wells is one or two, InGaAlP clad layers formed above andbelow the active layer, and light reflecting layers formed, in astacking direction of the active layer, further above and below the cladlayers through the respective clad layers.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described with reference to the drawings, which arepresented for the purpose of illustration only and are in no waylimiting of the invention.

FIG. 1A is a perspective view showing a configuration of a surfaceemitting semiconductor laser involving a first embodiment of the presentinvention;

FIG. 1B is an enlargement of a portion of the active layer and cladlayers shown in FIG. 1A;

FIG. 1C is an energy band diagram of the active layer and clad layersshown in FIG. 1B.

FIG. 2 is a diagram showing simulation results of the threshold currentand the maximum light output when the number of the wells and the wellwidth of the active layer and compositions of the clad layers involvingthe present embodiment are varied.

FIG. 3A is a perspective view showing a configuration of a surfaceemitting semiconductor laser involving a second embodiment of thepresent invention;

FIG. 3B is a sectional view cut along an A-B profile of FIG. 3A.

FIG. 4A is a perspective view showing a configuration of a surfaceemitting semiconductor laser involving a third embodiment of the presentinvention;

FIG. 4B is a sectional view cut along an A-B profile of FIG. 4A.

FIG. 5 is a perspective view showing a configuration of a surfaceemitting semiconductor laser involving a fourth embodiment of thepresent invention.

FIG. 6A is a perspective view showing a configuration of a surfaceemitting semiconductor laser involving a fifth embodiment of the presentinvention;

FIG. 6B is a sectional view cut along an A-B profile of FIG. 6A.

FIG. 7A is a perspective view showing a configuration of a surfaceemitting semiconductor laser involving a sixth embodiment of the presentinvention;

FIG. 7B is a sectional view cut along an A-B profile of FIG. 7A.

FIG. 8A is a perspective view showing a configuration of a surfaceemitting semiconductor laser involving a seventh embodiment of thepresent invention;

FIG. 8B is a sectional view cut along an A-B profile of FIG. 8A.

FIG. 9A is a perspective view showing a configuration of a surfaceemitting semiconductor laser involving an eighth embodiment of thepresent invention;

FIG. 9B is a sectional view cut along an A-B prolile of FIG. 9A.

FIG. 10A is a perspective view showing a configuration of an existingsurface emitting semiconductor laser;

FIG. 10B is an enlargement of a portion of the active layer and the cladlayers shown in FIG. 10A;

FIG. 10C is an energy band diagram of the active layer and clad layersshown in FIG. 10B.

DETAILED DESCRIPTION

(Explanation of Embodiments)

The present invention, while securing a gain, enables to make thinnerthe thickness of the active layer and to suppress heat generation fromthe active layer. As a result, an increase of the threshold current atthe high temperature operation may be suppressed from occurring, therebythe high temperature properties being improved.

In one embodiment of the present invention, as the clad layers, anIn_(0.5)(Ga_(1−x)Al_(x))_(0.5)P film (herein, x≧0.8) may be cited.Therewith, current confinement in the active layer may be improved,resulting in enabling to lower the threshold current, thereby animprovement of the high temperature properties being attained.

In another embodiment of the present invention, the light reflectinglayer is the DBR multi-layer film where a Ga_(1−x)Al_(x)As film (herein,0.9≧x≧0.5) and a Ga_(1−y)Al_(y)As film (herein, y≧0.9) are repeatedlystacked in turn. Thereby, light loss in the light reflecting layer maybe decreased, the threshold current being lowered and the hightemperature properties being improved. Furthermore, the light reflectingfilm is formed continuously with the active layer and the clad layers inthe same furnace. That is, the light reflecting layer may be formedwithout exposing to an ambient atmosphere. Accordingly, the lightreflecting layer may be improved in its quality and fabricatingprocesses thereof may be simplified.

In addition, as still another embodiment of the present invention, thelight reflecting layer is the DBR multi-layer film where anIn_(0.5)(Ga_(1−x)Al_(x))_(0.5)P film (herein, x≦0.5) and anIn_(0.5)(Ga_(1−y)Al_(y))_(0.5)P film (herein, y≧0.9) are repeatedlystacked in turn. Thereby, the light reflecting layer may be formed ofthe material of the same system with the active layer and the cladlayers. Accordingly, the light reflecting layer of low loss may beformed with ease.

As another embodiment of the present invention, the light exit window oflaser light that is exited transmitting through one of the above andbelow light reflecting layers is arranged in array on the substrate.Thereby, it needs only to pattern the light exit window to integrate aplurality of semiconductor lasers on the same substrate. Accordingly,application to a multi-link and so on may be implemented with ease.

As still another embodiment of the present invention, the DBRmulti-layer film includes a circular high resistance region. A currentsupplied to the active layer due to the circular high resistance regionmay be blocked and confined, thereby light emission efficiency beingimproved and the threshold current being lowered.

As another embodiment of the present invention, the DBR multi-layer filmincludes therein an AlAs layer, the AlAs layer being circularlysurrounded by an oxide region of AlAs. Due to the circular oxide region,the current supplied to the active layer may be blocked and confined,thereby light emission efficiency being improved and the thresholdcurrent being lowered.

Furthermore, as another embodiment of the present invention, on a side,different from the aforementioned clad layer side, of one of the lightreflecting layers that are the DBR multi-layer films, an electrode layertransmitting the output laser light is provided. Thereby, the currentmay be smoothly supplied from the electrode layer.

Furthermore, as still another embodiment of the present invention, on aside, different from the aforementioned clad layer side, of one of thelight reflecting layers that are the DBR multi-layers, a substrate isprovided, the substrate being hollowed to form the light exit window. Inthat case, a side opposite to the substrate may be made a mounting face,thereby, a distance from the mounting face to the active layer becomingshorter, resulting in an improvement of heat dissipationcharacteristics.

As another embodiment of the present invention, the DBR multi-layer iscircularly surrounded by a buried layer. The current supplied to theactive layer may be blocked and confined by the circularly buried layer,thereby light emission efficiency being improved and the thresholdcurrent being lowered.

Furthermore, as another embodiment of the present invention, the upperand lower DBR multi-layer films each that are the above and below lightreflecting layers include therein an AlAs layer, the AlAs layer beingcircularly surrounded by an oxide region of AlAs. Here, in place ofAlAs, InAs may be used. Thereby, due to the circular oxide region, thecurrent supplied to the active layer may be blocked and confined aboveand below the active layer, thereby, furthermore, light emissionefficiency being improved and the threshold current being lowered.

In the following, the surface emitting semiconductor laser involving theaforementioned embodiments will be explained with reference to thedrawings.

FIG. 1A is a perspective view showing a configuration of a surfaceemitting semiconductor laser involving a first embodiment of the presentinvention. In FIG. 1A, on an n-GaAs substrate 1, a DBR multi-layer film2, an n-InGaAlP clad layer 3, an MQW active layer 4, a p-InGaAlP cladlayer 5, a DBR multi-layer film 6, and a p-GaAs cap layer 7 are stackedin turn.

The active layer 4 and the clad layers 3 and 5 form a resonator of thesurface emitting semiconductor laser, at the active layer 4 in thecenter thereof a film thickness being designed to be an antinode of astanding wave of one wavelength.

The formation of these films may be implemented by means of for instanceMOCVD (Metal-Organic Chemical Vapor Deposition), MBE (Molecular BeamEpitaxy), or ALE (Atomic Layer Epitaxy).

In addition, on the back-face of the n-GaAs substrate 1, an n-sideelectrode 8 is formed, and on the p-GaAs cap layer 7, the p-sideelectrode 9 is formed. Furthermore, there is formed a disc-like openingin the p-GaAs cap layer 7 and the p-side electrode 9 to form the lightexit window 10 for taking out exit light. The p-GaAs cap layer 7 and thep-side electrode 9, by use of photoresist formed by means ofphotolithography as a mask, are selectively etched out to form lightexit window 10.

The active layer 4 is formed of for instance anIn_(0.5)Ga_(0.5)P/In_(0.5)(Ga_(0.5)Al_(0.5))_(0.5)P film; the clad layer3 being formed of for instance an n-In_(0.5)(Ga_(0.2)Al_(0.8))_(0.5)Pfilm; the clad layer 5 being formed of for instance ap-In_(0.5)(Ga_(0.2)Al_(0.8))_(0.5)P film.

Furthermore, the DBR multi-layer films 2 and 6, in which a film of highrefractive index and a film of low refractive index are repeatedlystacked in turn, are preferable to be formed by repeatedly stacking aGa_(1−x)Al_(x)As film (herein, 0.9≧x≧0.5) and a Ga_(1−y)Al_(y)As film(herein, y≧0.9) in turn.

For instance, the DBR multi-layer film 2 may be formed of 54.5 pairs ofn-Ga_(0.5)Al_(0.5)As/Ga_(0.5)Al_(0.95)As films, the DBR multi-layer film6 being formed of 34 pairs of p-Ga_(0.5)Al_(0.5)As/Ga_(0.05)Al_(0.95)Asfilms.

FIG. 1B is an enlargement of a portion of the active layer and the cladlayers in FIG. 1A. As shown in FIG. 1B, in the MQW active layer 4, anIn_(0.5)(Ga_(0.5)Al_(0.5))_(0.5)P film 4 a and an In_(0.5)Ga_(0.5)P film4 b are repeated stacked in turn; as shown in FIG. 1C, in a portion ofthe In_(0.5)Ga_(0.05)P film 4 b, a quantum well QW is formed.

In the figure, the well width Hb is set in the range of from 4 nm to 6nm, and the number of the wells Wn being set at one or two. A wellspacing Ha is preferably set in the range of from approximately 3 to 10nm.

The clad layers 3 and 5 are preferably formed of anIn_(0.5)(Ga_(1−x)Al_(x))_(0.5)P film (herein, x≧0.8), being formed of ann-In_(0.5)(Ga_(0.2)Al_(0.8))_(0.5)P film for instance.

FIG. 2 is a diagram showing simulation results of the threshold currentand the maximum light output when the number of the wells and the wellwidth of the active layer and the composition of the clad layersinvolving the present embodiment are varied. In FIG. 2, in the case ofthe composition of the clad layers 3 and 5 beingIn_(0.5)(Ga_(0.3)Al_(0.7))_(0.5)P and the well width Hb of the activelayer 4 being 7 nm, as the number of the wells Wn is increased from oneto five, the maximum light output decreases, in particular, when atemperature is elevated (from 50° C. to 70° C.), the maximum lightoutput decreases. Furthermore, the threshold current, whileapproximately constant when the number of the wells Wn is increased fromone to three, increases when the number of the wells Wn is increasedfrom three to five, in particular, when the temperature is raised (from50° C. to 70° C.), this tendency becomes remarkable.

Furthermore, in the case of the well width of the active layer Hb being5 nm, when the number of the wells Wn is increased from one to two, themaximum light output once increases, thereafter, as the number of thewells is increased from two to seven, the maximum light outputdecreases. In particular, when the temperature is raised (from 50° C. to70° C.), the maximum light output decreases. In addition, while thethreshold current, in the case of the number of the wells Wn being fromone to three, is approximately constant, when the number of the wells Wnis increased from three to seven, the threshold current increases, inparticular, when the temperature is raised (from 50° C. to 70° C.), thistendency becomes conspicuous.

Furthermore, in the case of the composition of the clad layers 3 and 5being changed from In_(0.5)(Ga_(0.3)Al_(0.7))_(0.5)P toIn_(0.5)(Ga_(0.2)Al_(0.8))_(0.5)P, when the case where the well width Hbof the active layer is 5 nm and the number of the wells Wn is two istaken for comparison purpose, at both temperatures of 50° C. and 70° C.,the maximum light output increases and the threshold current becomeslower.

Accordingly, when the well width of the active layer 4 is from 4 nm to 6nm and the number of the wells is from one to three, especially when oneor two, even under high temperature operation, while suppressing theincrease of the threshold current, the maximum light output may besuppressed from lowering.

Furthermore, by increasing the content of Al in the clad layers 3 and 5to make the band gaps thereof larger, the current confinement in theactive layer 4 may be improved. Thereby, the threshold current may belowered and the maximum light output may be increased.

In the aforementioned embodiment, a case where the p-side electrode 9 isformed in the surroundings of the light exit window 10 is taken by wayof illustration. However, a transparent electrode may be formed on thelight exit window 10. Thereby, into the active layer 4 below the lightexit window 10, the current may be efficiently injected to lower thethreshold current.

Still furthermore, it is explained that, by increasing the content of Alin the clad layers 3 and 5 to make the band gaps thereof larger, thecurrent in the active layer 4 may be effectively confined. However, byforming the clad layers 3 and 5 into a superlattice structure to formmulti-quantum barrier (MQB) and thereby causing electrons tending todrain out of the active layer 4 to reflect resonantly, the band gaps ofthe clad layers 3 and 5 may be effectively increased. That is, themulti-quantum barrier (MQB) may be adopted.

Furthermore, in the active layer 4, a distorted quantum well structuremay be introduced. Thereby, the threshold current may be lowered.

Furthermore, the active layer 4, other than the InGap/InGaAlPmulti-layer film, may be an InGaAlP/InGaAlP multi-layer film.

Furthermore, the DBR multi-layer films 2 and 6, other than GaAlAs/GaAlAsmulti-layer film, may be one formed by repeatedly stacking anIn_(0.5)(Ga_(1−x)Al_(x))_(0.5) P film (herein, x ≦0.5) and anIn_(0.5)(Ga¹⁻⁴Al_(y))_(0.5) P film (herein, y≧0.9) in turn, therebyalso, the reflecting film of low loss being formed with ease.

FIG. 3A is a perspective view showing a configuration of a surfaceemitting semiconductor laser involving the second embodiment of thepresent invention; FIG. 3B is a sectional view cut along an A-B profileof FIG. 3A. In FIGS. 3A and 3B, on the p-GaAs cap layer 7, the p-sidering electrode 11 is formed, by removing the p-GaAs cap layer 7 insideof the p-side ring electrode 11, the light exit window 10 being formed.

In addition, outside of the p-side ring electrode 11, extending to thep-GaAs cap layer 7 and the DBR multi-layer film 6, a high resistanceregion 12 is formed. The high resistance region 12 may be formed byselectively implanting ions such as protons to the outside of the p-sideelectrode 11, for instance.

The disposition of the high resistance region 12 enables to block andconfine the current 16 supplied from the p-side ring electrode 11 at theportion of the high resistance region 12, thereby light emissionefficiency being improved and the threshold current being lowered.

In the aforementioned embodiment, a method by which the high resistanceregion 12 is formed in the p-GaAs cap layer 7 and the DBR multi-layerfilm 6 is explained. However, the high resistance region 12 may beadditionally formed inside the clad layer 5, thereby the current beingfurther blocked.

FIG. 4A is a perspective view showing a configuration of a surfaceemitting semiconductor laser involving the third embodiment of thepresent invention; FIG. 4B is a sectional view cut along an A-B profileof FIG. 4A. In FIGS. 4A and 4B, the DBR multi-layer film 6 and thep-GaAs cap layer 7 are etched to be cylindrical. On the p-GaAs cap layer7, a p-side ring electrode 13 is formed, and the p-GaAs cap layer 7inside of the p-side ring electrode 13 is removed. Thereby, the lightexit window 10 is formed.

Furthermore, one or a plurality of AlAs layers 14 is formed on anylayers of the DBR multi-layer film 6. The AlAs layer 14 is exposed to anoxidizing atmosphere to oxidize a periphery portion of the AlAs layer14. Thereby, a selectively oxidized ring-like region 15 may be formedinside the DBR multi-layer film 6.

By disposing the selectively oxidized region 15, the current 16 suppliedfrom the p-side ring electrode 13 may be blocked and confined by theselectively oxidized region 15, thereby light emission efficiency beingimproved and the threshold current being lowered.

FIG. 5 is a perspective view showing a configuration of a surfaceemitting semiconductor laser involving the fourth embodiment of thepresent invention. In FIG. 5, on a single n-GaAs substrate 1, aplurality of light exit windows 10 is formed in array, from the lightexit windows 10 each, light being separately and independently takenout. The array-like surface emitting semiconductor laser, by changingonly the mask pattern, may be formed with ease. Accordingly, positioningbetween pellets each other and mounting processes may be eliminated whenarranging the semiconductor laser in array, resulting in simplificationof the fabricating process.

Furthermore, because the plurality of light exit windows 10 is formed onthe single substrate, optical components such as optical fiber andlenses may be three-dimensionally mounted with ease, being easilyapplied to the multi-link or the like.

FIG. 6A is a perspective view showing a configuration of a surfaceemitting semiconductor laser involving the fifth embodiment of thepresent invention; FIG. 6B is a sectional view cut along an A-B profilein FIG. 6A. In FIGS. 6A and 6B, on the DBR multi-layer film 6, atransparent electrode 61 is formed. The transparent electrode 61, an ITO(Indium Tin Oxide) film for instance, is one high in transmittance in anwavelength from 600 nm to 700 nm for instance.

In the DBR multi-layer film 6, the circular high resistance region 12 isformed. An inside shape of the high resistance region 12, while depictedas a prism in FIG. 6A, may be formed in cylinder. The high resistanceregion 12 may be formed by selectively implanting ions such as protonsor the like into the region for instance. From a region surrounded bythe high resistance region 12, in an upward direction in the drawing,laser light is exited.

The disposition of the high resistance region 12 enables to block andconfine the current 16 supplied from the transparent electrode 61 at theportion of the high resistance region 12. In addition, since thetransparent electrode 61 is formed over an entire surface of the DBRmulti-layer film 6, the current may be efficiently injected into theactive layer 4. Thereby, the light emission efficiency may be improvedand the threshold current may be lowered.

In the aforementioned embodiment, the method where the high resistanceregion 12 is formed inside the multi-layer film 6 is explained. However,the high resistance region 12 may be additionally disposed inside of theclad layer 5, thereby the current being further blocked and confined.

FIG. 7A is a perspective view showing a configuration of a surfaceemitting semiconductor laser involving the sixth embodiment of thepresent invention; FIG. 7B being a sectional view cut along an A-Bprofile of FIG. 7A. In FIGS. 7A and 7B, on the DBR multi-layer film 2the p-side electrode 9 is formed, on the back side of the substrate 1 ann-side electrode 8 being fanned.

In the DBR multi-layer film 2, the high resistance region 12 such asexplained in the third and sixth embodiments is formed to block andconfine the current injected from the p-side electrode 9. In the n-sideelectrode 8 and the substrate 1, a disc-like opening is formed to formthe light exit window for taking out emitted light. By selectivelyetching out the n-side electrode 8 and the substrate 1 with thephotoresist formed by means or photolithography as a mask, the lightexit window may be formed.

In the present embodiment, the current to the active layer 4 suppliedfrom the p-side electrode 9 may be blocked due to the high resistanceregion 12. Thereby, the light emission efficiency may be improved, andthe threshold current is lowered. In addition to the above, since thep-side electrode 9 side is used for mounting, a distance between theactive layer 4 and the mounting face becomes shorter to be excellent inheat dissipation characteristics. Accordingly, the temperaturecharacteristics may be improved.

In the aforementioned embodiment, the high resistance region 12 isformed inside of the DBR multi-layer film 2. However, the highresistance region 12 may be additionally formed inside of the clad layer5, thereby the current being further blocked and confined.

FIG. 8A is a perspective view showing a configuration of a surfaceemitting semiconductor laser involving the seventh embodiment of thepresent invention; FIG. 8B is a sectional view cut along an A-B profileof FIG. 8A. In FIGS. 8A and 8B, on the p-GaAs cap layer 7 the p-sidering electrode 11 is formed, and by removing the p-GaAs cap layer 7inside of the p-side ring electrode 11 the light exit window 10 isformed.

Furthermore, outside of the p-side ring electrode 11, extending to partof the clad layer 5 an n-type buried layer 81 is formed. The n-typeburied layer 81 may be formed in the following way, for instance. Thatis, the outside of the p-side ring electrode 11 is selectively etchedextending to the part of the clad layer 5 to form a recess, in therecess an n-semiconductor layer whose refractive index is lower thanthat of the clad layer 5 being regrown.

By disposing the n-type buried layer 81, the current 16 supplied fromthe p-side ring electrode 11 may be blocked and confined at the n-typeburied layer 81, thereby light emission efficiency being improved, thethreshold current being lowered.

FIG. 9A is a perspective view showing a configuration of a surfaceemitting semiconductor laser involving the eighth embodiment of thepresent invention; FIG. 9B is a sectional view cut along an A-B profileof FIG. 9A. In FIGS. 9A and 9B, the p-GaAs cap layer 7, the DBRmulti-layer film 6, the clad layer 5, the active layer 4, the clad layer3, and almost all of the DBR multi-layer film 2 are cylindrically etchedto form. On the p-GaAs cap layer 7, the p-side ring electrode 13 isformed and, by removing the p-GaAs cap layer 7 inside of the p-side ringelectrode 13 the light exit window 10 is formed. Instead of theaforementioned cylindrical etching, the p-side ring electrode 13 may beformed in rectangle and prismatic etching may be implemented.

On the DBR multi-layer films 6 and 2, one or a plurality of AlAs layers14 and 92 is formed, respectively. The AlAs layers 14 and 92 are exposedto an oxidizing atmosphere to oxidize the periphery thereof 14 and 92,thereby forming selectively oxidized ring regions 15 and 91 inside ofthe DBR multi-layer films 6 and 2.

By disposing the selectively oxidized regions 15 and 91, the current 16supplied from the p-side ring electrode 13 may be blocked and confinedby the selectively oxidized region 15, and the current flowing from theactive layer 4 to the n-side electrode 8 may be blocked and confined bythe selectively oxidized region 91. Thereby, the light emissionefficiency may be further improved, and the threshold current may befurther lowered.

The AlAs layers 14 and 92 may be an InAs layer.

In the above embodiments each, cases where the DBR multi-layer 6 isformed of compound semiconductors are explained for illustrationpurpose. However, other than this, with dielectrics for instance, theDBR multi-layer film of the similar function may be formed. In thatcase, dielectrics of high refractive index and low refractive index arealternately stacked. For the dielectrics, SiO₂, SiN_(x), amorphous Si,alumina and so on may be used.

In the above embodiments each, the surface emitting semiconductor laserswith the n-GaAs substrate 1 are explained. However, the conduction typemay be an opposite one.

It is understood that the invention is not confined to the particularimplementation modes set forth herein as illustrative, but embraces allsuch modified forms thereof as come within the scope of the followingclaims.

What is claimed is:
 1. A surface emitting semiconductor lasercomprising: an active layer having an InGaP/InGaAlP quantum wellstructure of which well width is from 4 nm to 6 nm and number of wellsis one or two; InGaAlP clad layers formed above and below the activelayer; and light reflecting layers that are stacked, in a stackingdirection of the active layer, through the above and below clad layerseach, further above and below the clad layers, wherein the lightreflecting layer each being a DBR multi-layer film in which aGa_(1−x)Al_(x)As film (herein 0.9≧x≧0.5) and a Ga_(1−y)Al_(y)As film(herein y≧0.9) are alternately stacked.
 2. A surface emittingsemiconductor laser as set forth in claim 1: wherein an exit window oflaser light outputted transmitting through one of the above and belowlight reflecting layers is formed in array on a substrate.
 3. A surfaceemitting semiconductor laser as set forth in claim 1: wherein the DBRmulti-layer film includes a circular high resistance region.
 4. Asurface emitting semiconductor laser as set forth in claim 3, furthercomprising: an electrode layer, on a side different from a clad layerside of one of the light reflecting layers that are the DBR multi-layerfilms, that transmits output laser light.
 5. A surface emittingsemiconductor laser as set forth in claim 3, further comprising: asubstrate on a side different from a clad layer side of one of the lightreflecting layers that are the DBR multi-layer films, the substratebeing hollowed to form a light exit window.
 6. A surface emittingsemiconductor laser as set forth in claim 1; wherein the DBR multi-layerfilm includes an AlAs layer therein, the AlAs layer being circularlysurrounded by an oxide region of AlAs.
 7. A surface emittingsemiconductor laser as set forth in claim 1: wherein one of the DBRmulti-layer films is circularly surrounded by a buried layer.
 8. Asurface emitting semiconductor laser as set forth in claim 1: whereinthe above and below DBR multi-layer films each that are the above andbelow light reflecting layers include an AlAs layer therein, the AlAslayer being circularly surrounded by an oxide region of AlAs.
 9. Asurface emitting semiconductor laser as set forth in claim 1: whereinthe above and below DBR multi-layer films each that are the above andbelow light reflecting layers include an InAs layer therein, the InAslayer being circularly surrounded by an oxide region of InAs.
 10. Asurface emitting semiconductor laser comprising: an active layer havingan InGaP/InGaAlP quantum well structure of which well width is from 4 nmto 6 nm and number of wells is one or two; InGaAlP clad layers formedabove and below the active layer; and light reflecting layers that arestacked, in a stacking direction of the active layer, through the aboveand below clad layers each, further above and below the clad layers,wherein the light reflecting layer each is a DBR multi-layer film inwhich an In_(0.5)(Ga_(1−x)Al_(x))_(0.5)P film (herein x≦0.5) and anIn_(0.5)(Ga_(1−y)Al_(y))_(0.5)P film (herein y≧0.9) are alternatelystacked.
 11. A surface emitting semiconductor laser as set forth inclaim 10: wherein the DBR multi-layer film includes a circular highresistance region.
 12. A surface emitting semiconductor laser as setforth in claim 11, further comprising: an electrode layer, on a sidedifferent from a clad layer side of one of the light reflecting layersthat are the DBR multi-layer films, that transmits output laser light.13. A surface emitting semiconductor laser as set forth in claim 11,further comprising: a substrate on a side different from a clad layerside of one of the light reflecting layers hat are the DBR multi-14yerfilms, the substrate being hollowed to form a light exit window.
 14. Asurface emitting semiconductor laser as set forth in claim 10: whereinthe DBR multi-layer film includes an AlAs layer therein, the AlAs layerbeing circularly surrounded by an oxide region of AlAs.
 15. A surfaceemitting semiconductor laser as set forth in claim 10: wherein one ofthe DBR multi-layer films is circularly surrounded by a buried layer.16. A surface emitting semiconductor laser as set forth in claim 10:wherein the above and below DBR multi-layer films each that are theabove and below light reflecting layers include an AlAs layer therein,the AlAs layer being circularly surrounded by an oxide region of AlAs.17. A surface emitting semiconductor laser as set forth in claim 10:wherein the above and below DBR multi-layer films each that are theabove and below light reflecting layers include an InAs layer therein,the InAs layer being circularly surrounded by an oxide region of InAs.18. A surface emitting semiconductor laser as set forth in claim 10:wherein an exit window of laser light outputted transmitting through oneof the above and below light reflecting layers is formed in array on asubstrate.